DESCRIPTION OF THE PSYCHROMETRIC CHART
The ASHRAE Psychrometric Chart is a graphical representation of the thermodynamic properties of air. There are five different psychrometric charts available and in use today:
Chart No. 1 — Normal temperatures, 32 to 100F Chart No. 2 — Low temperatures, –40 to 50F Chart No. 3 — High temperatures, 50 to 250F
Chart No. 4 — Normal temperature at 5,000 feet above sea level, 32 to 120F
Chart No. 5 — Normal temperature at 7,500 feet above sea level, 32 to 120F
Chart No. 1 can be used alone when no freezing temperatures are encountered. Chart No. 2 is very useful, especially in locations with colder temperatures. To apply the lower range chart to an HVAC system, part of the values are plotted on Chart No. 2 and the resulting information transferred to Chart No. 1. This is discussed in the EXAMPLES OF AIR MIXING PROCESS section. These two charts allow working within the comfort range of most systems. Copies are provided in the ASHRAE PSYCHROMETRIC CHARTS section.